Alkaline-Earth Metal Ca and N Codoped TiO2 with Exposed {001} Facets for Enhancing Visible Light Photocatalytic Activity

Alkaline-earth metal Ca and N codoped TiO2 sheets with exposed {001} facets were obtained through a one-step hydrothermal process. The codoped TiO2 appears as microsheets with length of 1-2 mu m and thickness of 100-200 nm. The X-ray diffractometer and X-ray photoelectron spectroscopy results confirm that Ca and N codoped TiO2 has higher crystallinity than N-doped TiO2, as well Ca, N atoms were successfully codoped into TiO2 as interstitial Ca and interstitial N or an O-Ti-N structure, respectively. Compared with N monodoped, further alkaline-earth Ca codoped has little influence on the energy bands of TiO2 except slightly elevating the conduction band edge at a value of 0.02 eV. The hydroxyl radicals (center dot OH) producing and photocatalytic experiment shows that Ca and N codoped can effectively decrease the generation of recombination centers, and enhance separation efficiency of photo-induced electrons and holes as well as the photocatalytic activity of TiO2. The codoped photocatalyst has the highest photocatalytic activity when Ca doped ratio reach 0.48%. Excess Ca doped will weaken the crystallization of anatase TiO2, form charge center, produce new recombination centers and finally reduce the photocatalytic activity of TiO2.